Polyvinylidene fluoride resin has been widely known as a resin having a ferroelectric property, and has been used for pyroelectric sensors, acoustic sensors, speakers and so on, taking advantage of the property of the resin. In recent years, examination is carried out for application to recording devices which utilize the ferroelectric property of the resin. For example, optical memory devices utilizing the ferroelectric property of polyvinylidene fluoride resin have been proposed (Japanese Patent Laid-open No.SHO 55-126905, Japanese Patent Laid-open No.SHO 59-215096, Japanese Patent Laid-open No.SHO 59-215097, Japanese Patent Laid-open No.SHO 64-16853, Japanese Patent Laid-open No.HEI 1-256047, Japanese Patent Laid-open No.HEI 1-256098). Moreover, ferroelectric memories using polyvinylidene fluoride resin (Japanese Patent Laid-open No.SHO 61-48983, Japanese Patent Laid-open No.HEI 6-150684, PCT International Publication No. WO99-12170) and an active matrix substrate using polyvinylidene fluoride resin (Japanese Patent Laid-open No.HEI 1-167732) have also been proposed.
In using polyvinylidene fluoride resin for the above mentioned purposes, there is an advantage that a mass storage medium can be obtained easily. In order to give a ferroelectric property to a polyvinylidene fluoride copolymer, polarization is necessary. When thin films are made remarkably thinner in order to increase the capacity, there is also an advantage that voltage used for polarization can be made low. Furthermore, there is also an advantage that the bit density (packing density) can be improved by laminating the thin films
However, there is a problem in that it is difficult for the polyvinylidene fluoride resin to form a uniform thin film. Especially, in the case in which thin films and electrodes are formed and laminated on a semiconductor substrate or a metal substrate, a homogeneous laminated product cannot be obtained unless the thin films are uniform. When high electric field is applied on an uneven thin film, the problem of short-circuit or the properties within the thin film becoming uneven will arise.
The present invention has been accomplished to solve the above problems in thin film formation of polyvinylidene fluoride resin, and an object of the present invention is to provide a polyvinylidene fluoride copolymer capable of forming a uniform thin film and also to provide a solution of the copolymer. Another object of the present invention is to provide a thin film comprising a polyvinylidene fluoride copolymer and to provide a ferroelectric thin film of a polyvinylidene fluoride copolymer, in which the thin film is polarized.